A clamping unit for a chuck of a machine tool spindle contains a threaded shaft for adjusting the clamping jaws of the chuck. The threaded shaft is axially adjustable in the clamping unit by means of a threaded nut connected to a rotor of a servomotor actuator. An electrically actuable, releasable clutch has a first clutch element, which is connected in a rotationally secure and axially displaceable manner to the threaded shaft, and a second clutch element, which cooperates with the first clutch element and is connected in a rotationally secure manner to the rotor. When the clutch is activated, the threaded shaft and the threaded nut are mutually connected in a rotationally secure manner and prevent axial displacement of the threaded shaft.

An adjustable chuck apparatus is provided with a torque limiting device; a torque transmitting mechanism; a chuck; a threaded fastener; a pin; a first positioning member including a threaded tunnel; a second positioning member including a threaded tunnel; a barbell shaped interconnection member including a first externally threaded section at one end and threadedly fastened in the threaded tunnel of the first positioning member, a second externally threaded section at the other end and threadedly fastened in the threaded tunnel of the second positioning member, a bar interconnected to the first externally threaded section and the second externally threaded section, and a hole element through the second externally threaded section; a truncated conic collet; and a cap. Each of different screw taps can be fastened by the apparatus by rotating a hand tool to adjust a distance between the first positioning member and the second positioning member.

A chuck including a chuck body that supports a plurality of jaws. An outer sleeve is axially fixed with respect to the chuck body. A nut is coupled to the outer sleeve, and the nut is movable axially and radially relative to the chuck body. The nut interacts with the jaws such that when the outer sleeve rotates, the nut moves axially and radially relative to the body.